Throw the $100 towards upgrades on the RC10, I don't see you being able to get a decent running rig for that much. With a hundred bucks your looking at a well used and probably abused rig, a lot of times Traxxas Nitro Sports and Rustlers can go for that cheap but will be older models and need work to get up and running. I don't know anything about your RC10 but you could get some different tires or some better servos, throw a rx pack and charger in if you're using AAs, and if you're still using a 27mhz radio you could jump up to a 2.4ghz setup.